Abstract

The U.S. Department of Energy (DOE) will remediate the high-level radioactive wastes (HLWs) stored in 177 aging underground storage tanks at the Hanford, Washington site. The retrieved wastes will be separated into a HLW stream containing most of the radionuclides and a low-activity waste (LAW) stream containing the bulk of the nonradioactive chemicals and the soluble components of the tank waste. Both waste streams will be vitrified. Pretreatment of the LAW stream is required to remove cesium-137, strontium-90, technetium-99, and transuranic elements.

This report provides information useful to U.S. Nuclear Regulatory Commission staff for understanding the technical bases of the pretreatment technologies proposed by DOE privatization contractors and for identifying potential hazards associated with those technologies. A review of publicly available information on the chemistry and technology of unit operations proposed by BNFL Inc. and by Lockheed Martin Advanced Environmental Systems is presented. These unit operations are sludge washing, ion exchange, electrochemical methods, organic destruction, and precipitation/filtration. The physicochemical bases of the unit operations and published experimental studies involving alkaline tank wastes are discussed. The proposed pretreatment technology is discussed in the context of its application to Hanford wastes, including operational and safety considerations.